Since the impinging signal sources in most RF environments are distributed over a very wide physical area, an RF survey concerned with signal sources within a limited physical region is difficult due to the effort of manually determining which signals are in the region of interest. Known patent documents include:                U.S. Pat. No. 4,353,073;        U.S. Pat. No. 4,903,333;        U.S. Pat. No. 6,218,987;        U.S. Pat. No. 6,664,921; and        U.S. Pat. No. 6,680,709.        